<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8" /> 
  </head>
  <body> 
    <canvas id="myCanvas" width="300" height="150" style="border: 1px solid #d3d3d3" ></canvas>

    <script>
      var myCanvas = document.getElementById("myCanvas");
      var ctx = myCanvas.getContext("2d");
      ctx.fillStyle = "#FF0000";
      ctx.fillRect(20, 20, 150, 100);
    </script>
  </body>
</html>
